Bad solenoid?

[ejay]

So I had a multi day trip planned with a friend, and at 5 am as we prepared to shove off, I turned the key and my late model A4 would not turn over, much like dead battery. I was crestfallen, as I had never had a problem with either dead batteries or any trouble with the starter.

My friend, who is a farmer, and works with tractors all the time, asked for a screwdriver and he jumped the solenoid connections and the engine fired up just fine. The A4 started up fine the the remainder of the trip, without any help.

Is my solenoid bad? Should I replace it?

[Dave Neptune]

First double check the key-switch to be sure the solenoid is getting a full voltage signal.
Did you wiggle and/or keep twisting the key to start? Sometimes a tap with a screw driver or lightly with a hammer will unstick the solenoid too. It is indicative of a sticky solenoid in need of replacement.

If voltage is good from the switch change out the solenoid, They can stick once in a while as they are in a nasty environment.

Dave Neptune

[Surcouf]

when you jump your solenoid this way, you do not just jump the solenoid itself, but also the contact coming from your ignition switch. Said differently, if jumping you solenoid made the trick, you could have an issue with your solenoid, or an issue with the wiring coming from your ignition key (switch if you have one). You would need to check if you get the voltage at the starting terminal of your solenoid when you turn the key to verify if the circuit works properly.

EDIT: Dave's answer is better...

[ejay]

Thanks so much for the input! I definitely did not jiggle the switch when we got it going.

I will try to check the voltage going to the solenoid. Excuse my ignorance, but should I use a multimeter to check voltage between the solenoid posts when somebody turns the key?

[Dave Neptune]

Yes and no, use the meter from the post to ground with the key at start. To check the key there are two tests first from the hot side to ground then from the "switched to start side" of the key switch when engaged in start. Voltage should be the same voltage.

Disconnect the positive wire from from the coil OR be sure and turn the key yo off so you don't fry the coil by forgetting.

Do close the intake water valve if you do any "cranking" so there's no water encroachment.

Dave Neptune

[Al Schober]

ejay,
Recommend you have a decent multimeter (one that you trust) on board and be familiar with its use. In the same Ziplock with the multimeter should be a ground cable, clips on each end, capable of reaching from your batteries to either end of the boat.
My meter came with probes having 45 degree points. I sharpened them to needles so I could just push them through insulation.
Our boat systems deal with a nominal 12V system. Some of the loads on the system are high current, which are sensitive to things like bad cables and bad connections.
For example, battery charging. You identify a problem (batteries take too long to charge) and want to fix the issue. Meter tells you the alternator is putting out 14.5 V but only 13.5 V is getting to the battery. A sensitive meter will allow you to check each cable and connection in the circuit. I personally have had cases of 1) too small a ground cable from the battery to the alternator, 2) a bad cable between the engine block and the battery negative, and 3) a bad ground connection between the alternator and the engine block (don't rely on the pivot bolt for a ground).
A multimeter can be your electrical friend.

[joe_db]

FYI -
I had ongoing occasional "no starts" where the ignition was on, but the solenoid would not engage. I now have the start button controlling a relay near the starter, the relay needs very little current to pull in and I have never had a problem starting since.